Space Amoeba

Origin

An exploratory mining rocektship from Earth lands on a "weird planet" looking for valuable ore. One of the miners by the name of Anderson wanders away from the ship while maintaining visual contact. Examining a deposit of titanium ore, he notices large Amoeba creatures. Three of the alien Amoeba take on his form. When he returns to the ship with the other three following him, they all claim to be Anderson. The captain chooses the right Anderson to let aboard. When asked how the captain knew, he told Anderson that he was the only one of the four who sweated.